A unique set of 11,008 onion expressed sequence tags reveals expressed sequence and genomic differences between the monocot orders Asparagales and Poales

Enormous genomic resources have been developed for plants in the monocot order Poales; however, it is not clear how representative the Poales are for the monocots as a whole. The Asparagales are a monophyletic order sister to the lineage carrying the Poales and possess economically important plants such as asparagus, garlic, and onion. To assess the genomic differences between the Asparagales and Poales, we generated 11,008 unique ESTs from a normalized cDNA library of onion. Sequence analyses of these ESTs revealed microsatellite markers, single nucleotide polymorphisms, and homologs of transposable elements. Mean nucleotide similarity between rice and the Asparagales was 78% across coding regions. Expressed sequence and genomic comparisons revealed strong differences between the Asparagales and Poales for codon usage and mean GC content, GC distribution, and relative GC content at each codon position, indicating that genomic characteristics are not uniform across the monocots. The Asparagales were more similar to eudicots than to the Poales for these genomic characteristics.     

Droplet-vitrification and morphohistological studies of cryopreserved shoot tips of cultivated and wild pineapple genotypes

Germplasm conservation of pineapple [Ananas comosus (L.) Mer.] is crucial to preserve the genus’ genetic diversity, to secure material for genetic improvement and to support innovative and new research. Long-term conservation is accomplished through cryopreservation, that is done by storing cells or tissues at ultra-low temperature in liquid nitrogen (−196 °C). Droplet-vitrification, a combination of droplet freezing and solution-based vitrification, was used to establish a protocol for cryopreservation of pineapple genetic resources. This protocol was tested on cultivated and wild pineapple genotypes to establish a long-term germplasm security duplicate as well as to investigate cryo-injuries in the tissues by means of histological techniques. Excised shoot tips (0.5–1 mm with one primordial leaf) of different pineapple genotypes were precultured for 48 h on solid MS medium containing 0.3 M of sucrose. Three PVS2 exposure times (30, 45 and 60 min) were tested. The results showed high post cryopreservation survival for all genotypes evaluated. The best PVS2 exposure time varied according to genotype, although 45 min gave the best survival for the majority of genotypes. The technique was highly efficient in cryopreserving meristem shoot tips of different pineapple genotypes, and was also less laborious than techniques previously reported. This is a first report on application of the droplet-vitrification technique to diverse genotypes of cultivated and wild pineapples and the first report on histological changes occurring in cryopreserved Ananas tissue.

     

Cryopreserved storage of clonal germplasm in the USDA National Plant Germplasm System

The US Department of Agriculture-Agricultural Research Service (USDA-ARS), National Plant Germplasm System (NPGS) plant collections are a critical source of genetic diversity for breeding and selection of improved crops, including vegetatively propagated plants. Information on these collections is readily accessible to breeders and researchers on the internet from the Germplasm Resources Information Network (GRIN). The clonal collections are at risk for loss due in part to their genetic diversity that makes growing them in one location a challenge, but also because it is difficult to have duplicate collections without incurring great expense. The development of cryopreservation techniques during the last two decades provides a low maintenance form of security backup for these collections. National plant collections for vegetatively propagated crop plants and their wild relatives are maintained by the USDA-ARS, NPGS at 15 sites across the country. These sites include various combinations of field, greenhouse, screenhouse, and in vitro collections. Cryopreserved backup collections in liquid nitrogen storage were instituted in the 1990s, increased greatly in the 2000s with the advent of new techniques, and are continuing today. Collections of dormant buds of temperate trees, shoot tips of in vitro cultures of many crops, and embryonic axes of some large seeded or recalcitrant seeded plants are all part of the clonal backup storage system.